Learn Portuguese (Portugal): A mulher mais rica do país vai comprar aquele prédio. - The richest woman in the country is going to buy that building.

In Portuguese, the relative superlative is usually formed by placing the definite article (a), the noun (mulher), then mais (most) or menos (least), and finally the adjective (rica). So, the phrase is literally structured as the woman most rich.

Why does the sentence use do país when the English translation says in the country?

When forming superlatives to say someone is the most or the least of a group or place, Portuguese uses the preposition de (of) rather than em (in). Since país is a masculine noun, de combines with the article o to become do. You are literally saying she is the richest woman of the country.

Why use aquele prédio for that building instead of esse prédio?

Portuguese has two main words for that. You use esse when the object is near the person you are listening to. You use aquele when the object is far away from both you and the listener, usually meaning that one over there.

Is vai comprar the normal way to say is going to buy or will buy?